It is well-known in the art to construct embankments from a variety of materials in connection with road construction and the like. On the one hand, it is desirable to construct such embankments with as steep a grade as possible to conserve space along the embankment. For example, in constructing a road many miles in length, the cost of acquiring a right-of-way even a few additional inches in width can be considerable. There are also important environmental and aesthetic factors which dictate minimizing the total width of the roadway and embankment. The method of this invention will conserve space when building roads through or along swamps or wetland areas, thus preserving valuable flood storage capacity and limiting desecration of these valuable areas.
On the other hand, the cost of acquiring a wider right-of-way and related factors must be balanced against the monetary and aesthetic costs of the alternative construction methods. Thus, for example, an elevated roadway could be constructed entirely on steel pilings and supports and thereby achieve essentially a 90.degree. embankment which uses the minimum amount of lateral space. Similarly, a depressed or below ground-level roadway could be constructed in a concrete culver and, again, achieve essentially a 90.degree. embankment. Not only are such constructions usually considered to be an eyesore, but they are also so expensive that their use is generally restricted to densely-populated urban areas where land values are sufficiently high to justify such uneconomical construction methods.
In the typical case, however, a trade-off must be made between the steepness of the embankment and the cost of construction. Where land is relatively inexpensive and plentiful, embankments may be constructed almost entirely from earth. Although such embankments gradually become stabilized by the growth of vegetation, initially such embankments cannot exceed a gradient of about 10.degree. without danger of erosion. Alternatively, embankments may be constructed from stones ranging in size from relatively small gravel-sized stones to large boulders. Although this type of material permits the construction of stable embankments having gradients of about 20.degree., this type of construction is also more expensive and produces a somewhat barren-looking landscape because the stone embankments cannot support vegetation.